Get First Or None

get_first_or_none.py

def get_first_or_none(qs):
    """
    Gets first item of queryset or None,
    queryset can be QuerySet, RelatedManager,
    Model, or object/Model instance.
    
    Examples:
        class Pizza(models.Model):
            name = models.CharField(max_length=50)
            toppings = models.ForeignKey('test.Topping')
            
        class Topping(models.Model):
            name = models.CharField(max_length=50)
        
        # related fields
        first_topping = get_first_or_none(self.toppings)
        # model
        my_pizza = get_first_or_none(Pizza)
        # queryset
        p = get_first_or_none(my_pizza.toppings.filter(name__istartswith='p'))
        # object, not useful here:
        first_pizza = get_first_or_none(my_pizza)
        
    """
    if isinstance(qs, models.query.QuerySet):
        try:
            return qs[:1][0]
        except IndexError:
            return None
    elif isinstance(qs, models.Manager):
        try:
            return qs.all()[:1][0]
        except IndexError:
            return None
    elif issubclass(qs, models.Model):
        try:
            return qs._default_manager.all()[:1][0]
        except IndexError:
            return None
    elif isinstance(qs, models.Model):
        # Probably not expected behavior, but could be
        # useful with setting `ordering` in your model's
        # Meta class.
        try:
            return qs._default_manager.all()[:1][0]
        except IndexError:
            return None
    else:
        return None